Is it better to upgrade this with a single 4GB DDR2 RAM fitting in one slot, or a kit of 2GB DDR2 RAMs fitting in both slots? I'm pretty sure it can handle 2GB in each slot but I'm not really sure it can handle the full 4GB all in one place. Yet it seems to be a more battery conscious decision to occupy only one ram slot (?).

Secondly, I wanted to ask your opinion on RAM speeds, would it be better to get the higher RAM speed (640Mhz) even though its full speed wouldn't be supported or would it be wiser to just go with the 533 Mhz RAM?

Thank you so much, I've done a lot of Googling on this but I'm still confused.

4 Answers
4

Speed
Your laptop FSB is 533MHz, so there is no reason of putting higher speed memory than 533MHz, except that you may find newer modules somewhat cheaper than the old ones (this may happen), but nothing bad will happen anyways.

Modules
Some (most?) laptops don't support 4Gb RAM modules. Be aware.. Since this mistake can cost you quite a bit, I'd recommend to go with 2x2Gb.

Power consumption
Sure, 1 memory module will eat less battery than 2, but the RAM power requirements are so tiny, so you will never notice any difference. Overall battery life difference will be just a second or something.
Main battery eaters are LCD screen, graphics card, fan, hard drive, which basically means, that if you switch to a fanless cpu (atom), choose the ssd drive, and will work with the closed lid on external monitor, you laptop will run several hours.

Whilst you can usually get away with using higher Mhz memory (usually the machine just under clocks), it is hard to say about the size of memory.

Usually manufacturers who do not sell in a configuration will say that in order to protect themselves just in case someone purchases memory and finds it does not work.

I would advise that you look at the chipset of your motherboard and try to find any other manufacturer that does state 4GB memory sticks work - if the answer is yes, most likely you will have no problem.

As for 1x4GB or kit - I would advise against going for a single or mixed configuration as you loose the dual channel ability which will slow the machine down (about 5%-20%).

Try to either get a matching stick of what you already have, or two of a new sort. As for buying kits, read this answer I wrote a while ago.

I just bought a 4GB PC 5200 module for my FSC Amilo XA 3530 laptop (introduction year 2008). Together with a 2GB mdoule I've 6GB ram in Windows and Linux 64bit. It shows me 6144MB ram in the bios. When I read the recommendation from crucial.com or FSC it's not possible. So FSC is silly about their own hardware.